1. Field of the Invention
The present invention relates to a calibration apparatus, a calibration method, and a testing apparatus. More particularly, the present invention relates to a calibration apparatus that calibrates a jitter measuring circuit for measuring a jitter in an input signal.
2. Related Art
There is considered a circuit for measuring a jitter in an on-chip mode as a circuit for measuring a jitter. For example, this circuit measures a jitter in a high frequency signal generated from the inside of chip, and converts jitter amplitude of the measured signal into voltage magnitude, in order to output the voltage magnitude to the outside of chip. It is possible to detect a jitter value outside the chip by dividing the voltage magnitude by jitter output gain of the jitter measuring circuit.
Jitter output gain of the jitter measuring circuit can use a designed value based on a circuit design. Moreover, as another method, there is also considered a method for supplying a signal having a known jitter from the outside of chip to the jitter measuring circuit and measuring output magnitude of the jitter measuring circuit.
However, as a process of manufacturing a semiconductor miniaturizes, characteristics of circuit elements such as a transistor, a resistor, capacitance, or the like in the jitter measuring circuit largely fluctuate according to the variation of process. For this reason, real jitter output gain has a large error for the designed value.
Moreover, in case of a method of inputting a signal having a known jitter from the outside of chip, it is necessary to input a signal having frequency equal to a high frequency signal on chip from the outside so that a characteristic of the jitter measuring circuit is equal to that when measuring a high frequency signal on chip. However, it is difficult to supply, e.g., a high frequency signal around several GHz from input pins of the chip into the chip.
Moreover, in this case, since the quality of high frequency signal easily degrades, jitter amplitude of a signal being input into the jitter measuring circuit is not equal to jitter amplitude of a signal injected from the outside of chip. For this reason, since jitter amplitude of a signal being really input into the jitter measuring circuit becomes uncertain, it is difficult to obtain jitter output gain with high precision.
Moreover, although jitter output gain can be obtained with high precision when a high frequency signal is input into the jitter measuring circuit without degrading signal quality, there is a problem that this method requires a great deal of design cost.